1. Field of the Invention
The present invention relates in general to a venting means for munitions such as artillery shells, bombs, rockets, torpedoes, and any other munition which is transported and/or stored without a fusing mechanism. This venting lifting plug comprises a lifting plug with a threaded ring that is eutectically bonded to the lifting plug. In order to maintain the thread engagement capabilities, the threaded rings external threads match the current lifting plugs thread design. In order to attach the threaded ring onto the lifting plug, the lifting plug needs to have its external thread design made smaller to match the threaded rings internal threads. When assembled, lifting plug and threaded ring will have the same external profile as the current lifting plug. Additionally, the threaded joint of the lifting plug and threaded ring will be sealed with a eutectic material. The eutectic seal is to allow the lifting plug portion to remove itself off the threaded ring and vent the cook-off gases from munitions when the energetics reaches a predetermined dangerous temperature. The lifting plug is used as a shipping means to not only lift the munitions but to also protect the munitions from the environment until the fuze is attached. In protecting the munitions until the fuze is attached also has a negative feature, it seals the munitions and its energetics and, under high temperatures, this detonates the munitions as if the fuze was there. This is a dangerous scenario and the proposed innovation allows for the lifting plug to be ejected from munitions to vent the energetics from going high order under these elevated temperatures and thus, the venting lifting plug concept.
2. Description of the Related Art
In general, munitions have operating temperatures between −60° F. to 160° F. In case of a fire, the temperature of the munition raises beyond a safe operating temperature of, for example, 160° F., and the energetics inside the munition phase change from solid to liquid causing an internal “hoop Pressure” that causes the munition to explode in a high order reaction. This reaction is undesired and if the internal hoop pressure could be relieved, the energetics would not undergo high order detonation but instead combustion rather than an explosion.
This phase change phenomena also creates an “hoop” pressure inside the munition that this innovation uses to release the lifting plug from the threaded ring. The “hoop” pressure rises as the temperature increases above the operating temperature of the munition. The lifting plug has a eutectic seal at the threaded joint between the lifting plug and the threaded ring. The eutectic seal is maintained until a specific temperature is reached at which point, the eutectic material phase changes from solid to liquid. At this point, any mechanical features that bond the lifting plug to the threaded ring are nullified, and the lifting plug is free to unthread itself from the threaded ring via the Hoop Pressure forces of the energetics within the munitions and thus not allowing the munition to have a high order reaction. In having the energetic reaction reduced to a combustion rather than a high order reaction allows for fire fighting efforts in what would normally be a hazardous environment. A firefighting capability is most useful for ship board fires as well as in ammunition depot fires.
The United States Department of Defense has mandated that munitions be designed to withstand unplanned stimuli and improve survivability throughout its life cycle. Specifically cookoff or temperatures higher than operating temperatures are one of these unplanned stimuli and the proposed innovation for the lifting plug addresses this issue. The U.S. Army and U.S. Marine Corps field artillery units are equipped with the M109A6 Self Propelled Howitzer, M198, and/or M777A2 Joint Lightweight Towed Howitzers which uses the M795 High Explosive (HE) projectile. This M795 projectile is a typical round that is packaged and transported with a lifting plug and before use, a fuze replaces the lifting plug to make the round ready for its mission. Additionally, there are other projectiles that use the lifting plug as a transport and drop indication means.
The severity of energetic reaction is known to be a function of explosive confinement in thick walled projectiles. In an elevated temperature scenario such as a fire, venting is critical to limit the warhead reaction to burning instead of transitioning to a high order explosion. Accordingly, projectile modifications are desired to incorporate a venting means for the energetics under these non operating temperature exposures. Since the M795 projectile utilizes a lifting plug shown in FIGS. 1A and 1B to seal the shell body and conduct logistical operations, this plug has been modified to permit projectile venting via the addition of a threaded ring and a eutectic seal between the lifting plug and the new threaded ring.
The prior art lifting plug is assembled where the fuze would be normally positioned in a munition. The thread engagement of the lifting plug is identical to the threads used on the fuze, so they are interchangeable.
Several different lifting plug designs have been developed and tested over the years. Venting and drop indicator features have always been a consideration but have not been successful in achieving both characteristics. The proposed innovation herein incorporates the venting and drop indicator features into a new and novel design. Prior art lifting plugs shown in FIGS. 2A and 2B are designed to be able to;                a. Support the weight of the round or pallet during transportation.        b. Deform or break if the round has been dropped with significant energy imparted to potentially cause structural damage to the ogive; thus giving a visual drop indicator.        c. Seal the round fuze cavity during the packaging transportation of the round until the fuze is assembled.        
The drop indicator capability is illustrated in FIGS. 2A and 2B.
The current lifting plug has a drop indicator safety feature that cannot be eliminated and/or modified because it is used to identify rounds that have the potential of detonating/“blowing up” within the Cannon Tube due to cracks in the energetic material.
Some lifting plug designs incorporated wax material that would soften at temperatures below the explosive reaction temperature to reduce confinement and prevent transition from deflagration to detonation, such as shown in FIG. 3. A meltable fuze plug demonstrated acceptable results. However, the change to meltable lifting plug has resulted in degradation in the structural integrity of the lifting plug and its ability to accurately indicate excessive force impact to the ogive. This premature lifting plug failure results in a lower projectile availability to the users if projectiles were to experience rough handling in transportation. Additionally, the larger the opening of the vent port being created, the more effective is the elimination of a potential high order reaction. History has proved that the wax material venting methods could not attain a large enough vent opening, and users have abandoned the use of such venting lifting plugs with a drop indicator. The proposed design alternative should give the best of all desired features, namely, a drop indicator and a venting Lifting Plug.
It is therefore an object of the present invention to provide a means for munitions to vent before the temperature and/or internal pressure reaches a high order detonation point ( either temperature or pressure).
It is another object of the present invention to provide a venting means that minimizes and/or eliminates high order detonations of munitions by creating an opening or an orifice in the munition at elevated temperatures.
It is yet another object of the present invention to provide an insensitive munition by providing a device for venting the munitions energetics, whereby to prevent detonation thereof.
It is still another object of the present invention to provide a lifting plug in threaded engagement with the threaded fuze cavity in the munition in which the lifting plug neck portion provides a visual indication of any rough handling which may have caused damage to the munition, and a method and apparatus for venting the munitions energetics which can be used in combination with the lifting plug.
It is another object of the present invention to provide a device for venting the internal pressure produced by the energetic confined within the munitions body which will allow for a pressure buildup as the temperature rises until a specific temperature is reached and, at this point, the eutectic will phase change from solid to liquid and thus allow the lifting plug to be removed from the threaded ring and munition.
It is still another object of the present invention to use the pressure forces created in the munition internal cavity by the temperature rise as the energetic material expands within the cavity and provides the force needed to automatically remove the lifting plug from the munitions when a predetermined temperature is reached.